In the preparation of nitrogen-containing polymers effective as dispersant viscosity index improvers for lubricating oils, and/or as detergent additives for gasolines, a polymer is prepared by solution polymerization of a monomer or monomers to result in a polymer cement (polymer in hydrocarbon solvent). Coupling may follow. The polymer is hydrogenated, and then treated for hydrogenation catalyst removal. In normal course, the next step is lithiation (metalation) to introduce numerous sites in the polymer for subsequent treatment with a suitably reactive nitrogen-containing organic compound to finally result in a polymer exhibiting effective dispersant and/or detergent properties.
However, a problem developed in the lithiation step. Commercially unacceptably high levels of lithiating agent were being consumed. The relatively high consumption of lithiating agent required use of excessive amounts lithiating agent in order to attain desired level of lithiation. Unless sufficient lithiation is attained, there are not sufficient sites in the polymer to react subsequently with the nitrogen-containing compound and the net result is that the polymer then does not exhibit sufficient dispersant activity or properties.
In order to have a reasonably economical process of producing the nitrogen-containing hydrogenated polymers, and to assure sufficient resulting activity therein, a method was needed to reduce the amounts of lithiating agent required.